1. Field of the Invention
This invention relates to an electromagnetic actuator for a vehicle engine and, more particularly, to an electromagnetic actuator having a detached lower collar for aligning the actuator with a bore in the cylinder head of the vehicle's engine.
2. Description of Related Art
A conventional electromagnetic actuator for opening and closing a valve of an internal combustion engine generally includes "open" and "close" electromagnets which, when energized, produce an electromagnetic force on an armature. The armature is biased by a pair of identical springs arranged in parallel. The armature is coupled with an inlet or outlet gas exchange valve of the engine. The armature rests approximately half way between the open and close electromagnets when the springs are in equilibrium. When the armature is held by a magnetic force in either the closed or opened position (at rest against the open or close electromagnet), potential energy is stored by the springs. If the magnetic force is shut off with the armature in the opened position, the spring's potential energy will be converted to kinetic energy of the moving mass and cause the armature to move towards the close electromagnet. If friction is sufficiently low, the armature can then be caught in the closed position by applying current to the close electromagnet.
The conventional electromagnetic actuator has a one-piece lower housing 10 (FIG. 1) wherein an alignment collar 12 of the housing 10 is used to align the actuator to a cylinder head concentric with a valve which is to be actuated, as well as to house a hydraulic a valve lash adjuster (HVA). Thus, the outer and inner diameter of the collar 12 must be made very precisely via machining operations after the housing is roughly formed. The machining operations increase the cost of the actuator. Another purpose of the alignment collar of the housing is to provide a passage to transport oil from the oil feed in the cylinder head to the HVA.
The alignment collar 12 of the actuator housing 10, together with the HVA, is not integrated into the cylinder head because the cylinder head bore must be large enough to provide clearance for the lower valve spring. The HVA diameter is much smaller than the diameter of the lower valve spring, and is kept as small as possible to reduce the moving mass of the valve train.
In addition, the geometry of the conventional one-piece actuator housing 10 is not conducive to maintaining a stable geometry and, as such, the housing 10 tends to distort somewhat after manufacturing as internal stresses relax. The distortion problem is exacerbated by the core installation and coil over-molding process, at which time a molten resin is injected under very high-pressure into the interior of the housing (after the lamination core and coil have been installed).
An assembly problem is also associated with the conventional one-piece housing 10. The HVA must be installed into a bore in the alignment collar 12 of the actuator housing 10 prior to the installation of the actuator into the cylinder head. With the head in its upright position, the HVA will tend to fall out of the actuator during installation. Some retention structures have been proposed to alleviate this problem such as a providing additional parts or features to retain the HVA. However, these techniques are costly. Another proposal to retain the HVA during assembly is to coat the HVA with grease prior to installation in the alignment collar. However, this approach may attract dust during assembly.
Accordingly, there is a need to provide an electromagnetic actuator which eliminates the above-mentioned manufacturing and HVA installation problems.